A vehicle wire harness could be deteriorated, or worn out, and allow a core wire thereof to have electrical contact with a body etc. and be short-circuited. Therefore, in order to protect smoking of the wire coating and a current control element (a switching element) due to such short-circuiting, a thermal fuse has conventionally been used. The thermal fuse detects an overheated state and breaks. However, as electric parts increase, use of such a thermal fuse has been arising a problem of maintaining a space for the thermal fuse to be mounted. Moreover, recovering after break requires replacing with a new thermal fuse, and thus maintenance is troublesome. Besides, in a case where current is repetitively applied to a load (such as a headlamp) that has large inrush current, the thermal fuse tends to be deteriorated, and the breaking time thereof becomes shorter. Moreover, while the breaking time varies due to an initial variation and the temperature-dependent properties, breaking shall not occur during normal operation. Accordingly, a thermal fuse having a current capacity larger to some extent has to be used. This accompanies a problem that a thicker wire that has a larger smoking current and can be protected by the thermal fuse has to be used.
Furthermore, in recent years, Patent Document Japanese Unexamined Patent Application H11-139223 has reported an art to attach a temperature sensor directly to the wire, to measure a temperature of the wire and, when the wire reaches an abnormal temperature, and to break an applied-current.